InvalidCastException Specified cast is not valid.

public void DestroyCities() //102
    { //103
        foreach(GameObject go in transform) //104
        { //105
            do {
                StartCoroutine(DestroyFastly(go));
            } while(go != null);
        }
    }

public void DestroyCities() //102
    { //103
        foreach(GameObject go in transform) //104
        { //105
            do {
                StartCoroutine(DestroyFastly(go));
            } while(go != null);
        }
    }